Urinary tract infections (UTIs) are the second most common bacterial infection and cause significant patient morbidity. Half of all women will suffer from at least one UTI during her lifetime, while 25% of these women will endure recurrent infections. Uropathogenic E. coli (UPEC) are the most common uropathogen, and the rate of antibiotic resistant strains is increasing rapidly, thus escalating the need for a vaccine to prevet recurrence of UTIs. UPEC exist as extracellular pathogens and form intracellular reservoirs that cannot be treated by antibiotics. Our studies will develop a live-attenuated vaccine. The optimal recurrent UTI vaccine would 1) elicit an antibody response to target lumenal bacteria, 2) promote cell mediated responses to target intracellular UPEC reservoirs and 3) produce a strong memory response. Preliminary data show UPEC induces a default humoral response upon infection that allows intracellular reservoirs to remain in the bladder and leads to recurrent infections. UPEC lipopolysaccharide (LPS) triggers and modulates innate immune responses, although its role in adaptive immune response is understudied. A mutant of UPEC with altered LPS vaccinates against UPEC challenges, and partially eradicates UPEC reservoirs, suggesting enhanced cell-mediated responses. It is well-known antigen presentation initiates and skews T cell responses, therefore we hypothesize other mutations of LPS structure modulate innate responses at the level of antigen presentation, thus can skew the adaptive immune responses and optimize vaccine properties. We will address this hypothesis through a systematic interrogation of LPS structural motifs and characterize key innate and adaptive immune responses to UPEC mutant at the level of APC function, T cell skewing and vaccine efficacy. These studies will increase our understanding of UPEC pathogenesis and provide critical pre-clinical data on novel vaccine candidates for urinary tract infections.